Unfortunately GEFs SVGWriter still extends Graphics rather than Graphics2D. Thats a great shame and a great deal of work to update.

There was some discusion on the ArgoUML dev list about trying to reuse batik to generate SVG and remove this issue from GEF/ArgoUML - http://argouml.markm​ail.org/search/?q=batik#query:batik%​20list%3Aorg.tigris.​argouml.dev+page:1+m​id:su53p4vf63ymco5p+​state:results